This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We previously reported a comparative study of the in vivo infectivity and pathogenicity of a CCR5-tropic SHIVSF162 P4 in rhesus and pig-tailed macaques. Results indicate that both rhesus and pig-tailed macaques are similarly susceptible to SHIVSF162 P4 infection by mucosal routes. However, SHIV replication was significantly more robust in pig-tailed macaques than in rhesus. Since, persistent viral infection has been correlated with broadening of neutralizing antibody responses, we continued to monitor the evolution of viral sequences and neutralizing antibody activities in a subset of infected pig-tailed macaques after the primary goal of this study was achieved. PBMC from some of these animals were sent to Dr. James Robinson at Tulane University to isolate neutralizing monoclonal antibodies against HIV-1. Preliminary data from Dr. Robinson indicate that some of these antibodies may recognize conformation-dependent epitopes against HIV-1 envelope. Further characterization of these antibodies is in progress.